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a-Hummocky-and swaley-like cross-stratification (HCS and SCS, respectively) in bituminous marls at the Nechit River 2 Section. b-Dyke (d), sill (s) and ptygmatic structures (p) within the Bituminous Marls in the Nechit River 2 Section.
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Eocene-Oligocene sedimentation in the external areas of the Moldavide Basin (Marginal Folds Nappe, Eastern Carpathians, Romania): sedimentological, paleontological and petrographic approaches
The Marginal Folds Nappe is one of the most external tectonic units of the Moldavide Nappe System (Eastern Carpathians), formed by Cretaceous to Tertiary flys...
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Context 1
... this facies association, sedimentary structures very sim- ilar to swaley and hummocky cross-stratification (SCS and HCS; Fig. 8a), together with parallel and low angle cross- bedding, and wavy ( Fig. 7a) and lenticular ( Fig. 6b) bedding are recognized. Some sandy injections as dykes, sills and ptygmatic structures of decimetric dimensions are sporadi- cally present (Nechit River 2 Section; Fig. ...
Context 2
... very sim- ilar to swaley and hummocky cross-stratification (SCS and HCS; Fig. 8a), together with parallel and low angle cross- bedding, and wavy ( Fig. 7a) and lenticular ( Fig. 6b) bedding are recognized. Some sandy injections as dykes, sills and ptygmatic structures of decimetric dimensions are sporadi- cally present (Nechit River 2 Section; Fig. ...
Context 3
... HCS-like structures ( Fig. 8a), which seems to be of scour-drape type, together with swaley cross-stratification are usually interpreted as indicating storm conditions in shelf environment above the storm wave base (Cheel & Leckie 1993). Anyway such hummocky morphology can also be de- veloped by hyperpycnal flows as "flood-generated delta front lobes" (Mutti et al. ...
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The work is devoted to the construction and calculations of a three-dimensional density model of the sedimentary filling of the Carpathian-Pannonian region in order to obtain a more detailed map of the residual gravity field (stripped gravity map). This research was facilitated by and in-depth analysis of a large amount of data highlighting the den...
In the Eastern Carpathians, the Moldavide Nappe Complex represents a complicated tectonic edifice formed by several tectonic units mainly consisting of Cretaceous to Tertiary flysch and molasse deposits, deformed and piled up during the Miocene closure of the Carpathian Flysch basin, as a consequence of the collision between the Tisza-Dacia block a...
Citations
... The interpreted salinity changes are important to acquire a better understanding of the organic matter preservation of the Menilite Formation, which is well known for its hydrocarbon potential (e.g., Wójcik-Tabol et al., 2022). The organic petrography in the Oligocene of the Carpathians' successions has been mainly used as an indicator of organic matter origin and hydrocarbon potential (Kruge et al., 1996;Puglisi et al., 2006;Miclȃus et al., 2009;Belkin et al., 2010;Waliczek and Więcław, 2012;Wójcik-Tabol, 2015, 2017Wendorff et al., 2017;Kosakowski et al., 2018;Ziemianin, 2018Ziemianin, , 2020Zielińska et al., 2020;Waliczek et al., 2022). ...
... During the Oligocene a thick sequence (500-600 m) of restricted shales with interbedded conglomerate and sandstone turbidites were deposited in the foreland basin. The shales are black, finely laminated and referred to as the "paper shales" or Dysodiles (Miclȃuș et al., 2009). Another characteristic facies are the silicolites ("menilites") formed by recrystallized siliceous planktonic organisms often found in meter scale beds (Tulan et al., 2020). ...
... The deep-water sandstones comprise two different petrofacies: quartz arenites (Kliwa Sandstone; Fig. 7a) and litharenites (Fusaru Sandstone; Fig. 7b ;Sȃndulescu, 1988;Sylvester and Lowe, 2004;Miclȃuș et al., 2009;Roban et al., 2022). The quartz-rich sandstones were sourced by alluvial fans and coastal deltas along the eastern platform (Figs. ...
The Eastern Carpathian fold and thrust belt of Romania is one of the oldest oil and gas producing
areas in the world. Numerous fields have been discovered in this region since the 1850s,
however, their distribution is irregular with most of them clustered in the Moinesti area. Our
analysis suggests that although aspects of hydrocarbon generation, reservoir presence and
quality are rather similar along the strike of the entire thrust belt, recent uplift and erosional
unroofing of the Carpathians ultimately controlled the preservation of oil and gas fields. Areas
with the highest amount of exhumation and associated trap breaching, seem to have suffered
more intense deformation due to late inversion, which in turn, reflects the rheology of the various
basement units of the East European Margin underlying the Carpathians.
... These bituminous shales form hydrocarbon source rocks, and their deposition continues up to the Early Miocene (Dicea, 1996;Popescu, 1995;Săndulescu, 1988). Oligocene anoxia conditions alternated with gravity-driven sedimentation in the form of masstransport deposits and sandy turbidites sourced from opposite margins of the foreland basin (Anastasiu et al., 1994;Miclăuș et al., 2009;Schieber et al., 2019). Several publications focused on the Polish Outer Carpathians described shallow-water facies co-eval to deep water deposits and interpreted on the basis of storm-generated structures and palaeontological data (e.g. ...
We present new sedimentologic, petrographic, paleontological, and detrital zircon U‐Pb data on late Oligocene ‐ early Miocene sedimentary rocks of the thin‐skinned thrust belt of East Carpathians. These data were acquired to reconstruct the sedimentary routing system for two compositionally different turbidite fans made of the regionally extensive Kliwa and Fusaru formations. On the eastern margin of the Moldavides foreland basin, large low‐gradient river systems draining the East European Platform provided well‐sorted quartz‐rich sand forming deltas on wide shallow shelves and thick Kliwa submarine fans. Due to the westward subduction of a thinned continental plate, the western basin margin was characterized by short, steep‐gradient routing systems where sediment transport to deep water was mainly through hyperpycnal flows. The Getic and Bucovinian nappes of the East Carpathians and the exhumed Cretaceous‐Early Paleogene orogenic wedge fed Fusaru fans with poorly‐sorted lithic sand. The Fusaru fans trend northwards in the foredeep basin having an elongate depocenter, interfingering and then overlapping on the distal part of the Kliwa depositional system due to the eastward advance of the Carpathian fold‐and‐thrust belt. A smaller sediment input is supplied by southern continental areas (i.e., Moesian Platform, North Dobrogea, and potentially the Balkans). In general, the sandstone interfingering between distinct basin floor fan systems is less well documented because the facies would be similar and there are not many systems that have a distinct sediment provenance like Kliwa and Fusaru systems. This case study improves the understanding of regional paleogeography and sedimentary routing systems and provides observations relevant here or elsewhere on the interfingering turbidite fan systems.
... Geophysical studies have inferred that the Vrancea seismogenic body (Fig. 1b) is derived from descending relic oceanic lithosphere, which implies that most of the 140-160 km of Miocene shortening is related to oceanic subduction (e.g., Bokelmann and Rodler, 2014 and references therein). In contrast, sediment provenance studies have shown that the source of thin-skinned Carpathian nappes sediments changed gradually during the Eocene-Oligocene from the hinterland Carpathian units to the external stable platforms (Sȃndulescu et al., 1981;Miclȃuș et al., 2009;Roban et al., 2020). This hypothesis agrees with a Miocene subduction of a thinned continental Carpathian embayment (e.g., Sȃndulescu and Visarion, 2000;Ustaszewski et al., 2008) and implies a mechanism where the Vrancea slab is mostly derived from subducted continental lithospheric mantle, while its overlying crust was accreted to the Carpathian orogen (e.g., Vogt et al., 2017). ...
The exhumation mechanism of orogens showing one structural vergence, or single-sided orogens, is still not fully understood due to their common transition from periods of high convergence to slab retreat. The overprinting of inherited nappe stacks by subsequent back-arc extension makes it difficult to assess the low amounts of contractional exhumation observed, which are furthermore difficult to interpret due to long residence times in partial retention zones of typical low-temperature thermochronology markers. This is the case in many orogens worldwide and is often observed in the Mediterranean area as well. One notable exception is the Romanian segment of the Carpathian Mountains, where the back-arc extension took place far from the location where the nappe stack formed. To understand the mechanics of contractional exhumation in this single-sided orogen, we generated a new high-resolution low-temperature (apatite fission-track and U-Th/He) thermochronological transect across the Southeast Carpathian nappe stack and its foreland. This new dataset and its correlation with previous exhumation and kinematic studies demonstrate that the gradual accretion of sediments and crustal material was associated with an exhumation that migrated progressively towards the foreland throughout the entire contractional history. The exhumation style changed when the thin-skinned deformation was interrupted by periods of crustal accretion, associated either with the late Eocene onset of continental collision or with the late Miocene locking of the subduction system. The generally accepted moments of onset and termination of slab retreat are not directly visible in available exhumation data of the Southeast Carpathians. Our results are in agreement with modelling studies, which inferred that the formation of single-sided collisional wedges is primarily controlled by the pre-existing rheology of continental plates and is associated with large amounts of continental subduction.
... Due to the high petroleum potential of these rocks, they have been intensively studied over the last three decades, especially in the fields of petroleum geology, geochemistry, sedimentology and tectonics (e.g. Koltun, 1992;ten Haven et al., 1993;Lafargue et al., 1994;Kruge et al., 1996;Bessereau et al., 1997;Rospondek et al., 1997;Köster et al., 1998a,b;Kotarba et al., 2007;Miclȃuş et al., 2009;Guerrera et al., 2012;Sachsenhofer et al., 2015;Kosakowski et al., 2018;Filipek et al., 2020). These works have demonstrated the strong facial and geochemical heterogeneity of the Menilite rocks, and therefore the complexity of their formation history and related hydrocarbon systems. ...
... The lithology of the investigated sections is displayed in Fig. 3. More comprehensive sedimentological and lithofacial characteristic of the Nechit section is provided by Miclȃuş et al. (2009) andFilipek (2020). ...
... This was suggested for the Western Paratethys at the end of the Early Oligocene when the Dynow Formation was deposited (NP23; Schulz et al., 2005). This scenario is consistent with rather shallow to moderate water depths, strong terrestrial supply, and high transport energy in the Vrancea basin, as postulated by Miclȃuş et al. (2009). These authors based their interpretation on the presence of sandstones with hummocky cross-stratification (also see Filipek, 2020), and the identification of a well-preserved fossilised flat fish in the Bituminous Marls Mb. (Baciu and Chanet, 2002). ...
The Menilite facies, representing the most prolific hydrocarbon source rocks in the Carpathian fold and thrust belt, has been studied in two outcrop sections of the Vrancea and Tarcău Nappes (Eastern Romania) with the aim of determining the depositional environment during the Early Oligocene in the Vrancea and Tarcău sub-basins of the Central Paratethys. The biomarker composition indicates spatial variability in organic matter sources with mainly algal (particularly diatoms and dinoflagellates) and bacterial contributions in both sub-basins. This is reflected by the occurrence of such biomarkers as triaromatic dinosteroids, C25 highly branched isoprenoid thiophenes, marine n-alkanes, hopanoids and monomethyl alkanes. Solely in the Vrancea domain, the input of terrigenous organic matter of higher plant origin can be anticipated from the presence of abietane-class biomarkers (conifer-derived) and oleanane (angiosperm-derived). Distinct nutrient availability related to different positions of individual sub-basins (i.e. shallower, temporarily eutrophic Vrancea sub-basin vs. open-marine mesotrophic Tarcău domain) is reflected by different paleoproductivity indicators, such as the total organic carbon content, hydrogen index and 17α-hopanes to steranes ratio.
Water column stratification with bottom water anoxia enhanced by bacterial sulfate reduction stretching into the chemocline, at least intermittently, is expressed by a characteristic tiny pyrite framboid distribution and the lack of bioturbation. However, molecular indicators (Pr/Ph ratio, C35 homohopane index) imply fluctuations of redox conditions with the dominance of dysoxic conditions, which may suggest the occasional oxidation of bottom waters linked to local upwelling. Early diagenetic organic matter transformations such as photodegradation taking place in the oxidised upper part of the water column could also have affected the biomarker distributions. The presence of aryl isoprenoids and Me,i-Bu-maleimides indicates periods of euxinic conditions within the photic zone only in the Vrancea sub-basin during the deposition of the Lower Menilite Member. This is probably related to freshwater incursions from the adjacent, at least partly emerged forebulge, as suggested by a high MTTC ratio and the occurrence of higher plant-derived organic matter.
... Some geophysical studies (e.g., Bokelmann & Rodler, 2014, and references therein) suggested that the seismically active Vrancea zone, associated with a positive P waves teleseismic mantle anomaly located beneath the southeastern Carpathians (for geometry and details, see Ismail-Zadeh et al., 2012;Martin & Wenzel, 2006), is derived from descending relict oceanic lithosphere, implying that the 140 -180 km of Miocene shortening is related to the subduction of oceanic lithosphere. However, this suggestion is in contrast with other geophysical and geological interpretations that propose a thinned-continental origin of at least the external part of Carpathians embayment forming the European passive continental margin, (e.g., Miclăuș et al., 2009;, and references therein). ...
Reconstructing orogenic systems made up dominantly by sediments accreted in trenches is challenging because of the incomplete lithological record of the subducted oceanic domain and its attached passive continental margin thrusted by collisional processes. In this respect, the remarkable ~600 km long continuity of sediments exposed in the Eastern Carpathian thin‐skinned thrust and fold belt and the availability of quantitative reconstructions for adjacent continental units provide excellent conditions for a paleogeographical study by provenance and sedimentological techniques constraining sediment routing and depositional systems. These sediments were deposited in the Ceahlău‐Severin branch of the Alpine Tethys Ocean and over its European passive continental margin. We report sedimentological, paleomagnetic, petrographic, and detrital zircon U‐Pb data of Lower Cretaceous sediments from several thin‐skinned tectonic units presumably deposited in the Moldavides domain of the Eastern Carpathians. Sedimentological observations in the innermost studied unit demonstrate that deposition took place in a deepwater basin floor sheets to sandy turbidite system. Detrital zircon age data demonstrate sourcing from internal Carpathian basement units. The sediment routing changes in more external units, where black shales basin floor sheets to sandy mud turbidites were sourced from an external, European continental area. Although some degree of mixing between sources located on both margins of the ocean occurred, constraining a relatively narrow width of the deep oceanic basin, these results demonstrate that the internal‐most studied unit was deposited near an Early Cretaceous accretionary wedge, located on the opposite internal side relative to the passive continental margin domain of other Moldavides units.
... In the Romanian Carpathians (and Romania in general), sand intrusions are an understudied topic. Whilst some injectites have been referred to in the Eastern Carpathians (Miclaȗşet al. 2009;Jankowski & Wysocka 2019) or ECBZ (Bercea et al. 2016;Tamas et al. 2016), in this paper we provide detailed field observations of their architecture to support subsurface interpretation, infer timing and mechanism of emplacement, their relationship with regional tectonics and their impact on the petroleum system. ...
Sand intrusions are commonly associated with hydrocarbon-bearing clastic reservoirs and they can host a significant part of the reserves. They modify the depositional sandbody architecture, and can have an impact on the petroleum system elements. Their significance and complex architecture is difficult to assess in the subsurface due to limited resolution of seismic or core data. Outcrop analogues are key to better understand these complex reservoirs.
In the Eastern Carpathians Bend Zone, the Oligocene and Lower Miocene succession offer spectacular exposures of deep-water siliciclastic rocks modified by remobilisation and sand intrusion processes. These rocks are also present in producing fields in this area.
Sills can be as thick as the depositional sandstones (~4 m), and sill-dominated outcrops can provide a net-to-gross (net sandstone to shale ratio) of about 35 - 50 %. We quantified their architecture, in a study of the timing and mechanism of emplacement, their relationship to regional tectonics and their impact on reservoir connectivity. The intrusions are interpreted to be syn-tectonic, related to the major mid-Miocene compression in this part of the Carpathian Mountain Belt.
The intrusions lead to a large increase in vertical and horizontal connectivity. Our results will help to improve reservoir characterisation and production in these reservoirs.
... The stratigraphic record shows some differences the petrofacies composition since the early Cretaceous, indicating sediment supplies from different sources. The internal deposits are characterized by immature sandstones, while the external ones by mature sandstones and green-schist clasts in coarser sediments (Miclăuș et al., 2009;Amadori et al., 2012). In the central part of the Moldavidian Basin (on the median Tarcău sedimentation area) both types of sandstones occur, so generating particular successions (mixed successions). ...
... The main terrigenous supplies from the Internal Domain (Dacides) indicates the beginning of Moldavidian Basin closure (Oligocene-early Miocene). The activation of the External Domain may be the result of forebulge migration and rising on the TESZ, giving rise to the source area of green-schist clasts (e.g., Miclăuș et al., 2009) belonging to External Domain. The older thick sandy flysch (Paleocene-Eocene) on the internal Tarcău sedimentation area may indicate older tectonic activity in the Internal Domain. ...
... Petrographic studies of coarse terrigenous deposits (Vinogradov et al., 1983;Grasu et al., 1988;Gigliuto et al., 2004;Puglisi et al., 2006;Miclăuș et al., 2009;Amadori et al., 2012) pointed out some differences in petrofacies composition since the early Cretaceous, indicating sediment supplies from different sources ( Table 2). ...
... The interval between 310 and 195 m contains frequent beds of Kliwa sandstones (Figs 3b, 9). These sandstones are considered to be deep-marine deposits (Kotlarczyk and Uchmann, 2012;Miclaus et al., 2009), although Dziadzio et al. (2006Dziadzio et al. ( , 2016 assumed a shallow-water depositional environment. In the present paper the conventional interpretation was followed, and the thick, laterally continuous sandstone beds were interpreted as deep-water deposits representing the transition from a deep-marine channel fill to a depositional fan lobe (e.g. ...
This study investigates the hydrocarbon potential of Oligocene–Miocene shales in the Menilite Formation, the main source rock in the Ukrainian Carpathians. The study is based on the analysis of 233 samples collected from outcrops along the Chechva River in western Ukraine in order to analyse bulk parameters (TOC, Rock‐Eval), biomarkers and maceral composition.
In Ukraine, the Menilite Formation is conventionally divided into Lower (Lower Oligocene), Middle (Upper Oligocene) and Upper (Lower Miocene) Members. The Early Oligocene and Early Miocene ages of the lower and upper members are confirmed by new nannoplankton data. The Lower Menilite Member is approximately 330 m thick in the study area and contains numerous chert beds and turbidite sandstones in its lower part together with organic‐rich black shales. The shales have a high content of silica which was probably derived from siliceous micro‐organisms. The TOC content of the shales frequently exceeds 20 wt.% and averages 9.76 wt.%. HI values range between 600 and 300 mgHC/gTOC (max. 800 mgHC/gTOC). The Middle Member contains thin black shale intervals but was not studied in detail. The Upper Member is about 1300 m thick in the study area and is composed mainly of organic‐rich shales. Chert layers are present near the base of the Member, and a prominent tuff horizon in the upper part represents a volcanic phase during shale deposition. The member grades into overlying molasse sediments. The average TOC content of the Upper Menilite succession is 5.17 wt.% but exceeds 20 wt.% near its base.
Low T max and vitrinite reflectance measurements for the Lower (419°C and 0.24–0.34 %R r , respectively) and Upper (425°C and 0.26–0.32 %R r , respectively) Menilite Member successions indicate thermal immaturity. Biomarker and maceral data suggest a dominantly marine (Type II) organic matter input mixed with varying amounts of land‐plant derived material, and indicate varying redox and salinity conditions during deposition.
Determination of the Source Potential Index (SPI) shows that the Menilite Formation in the study area has the potential to generate up to 74.5 tons of hydrocarbons per m ² . The Chechva River outcrops therefore appear to have a significantly higher generation potential than other source rocks in the Paratethys realm. These very high SPI values for the Menilite Formation may explain why a relatively small area in Ukraine hosts about 70% of the known hydrocarbon reserves in the northern and eastern Carpathian fold‐thrust belt.
... The study area is located in one of the outermost nappes of the Eastern Carpathians, the Vrancea Nappe ( Fig. 1), where the BMF reaches its maximum thickness of about 70 m. The Oligocene-Miocene sedimentary succession of the Vrancea Nappe was deposited on the internal flank of a prominent forebulge that also functioned as a source area that supplied coarse clastics, such as quartzose sands and gravels with greenchist clasts (Miclăuș et al., 2009). ...
... Disturbed bedding seen in Fig. 3E may record incipient creep by gravitational pull on slope deposited sediments. The presence of slump features in these strata has previously been reported by Miclăuș et al. (2009). Because these slumped deposits include marls that also form the remainder of the BMF, they imply that portions of the BMF were deposited in a slope setting. ...
The bituminous marl formation (BMF) is an important source rock in Romania. At the study location, in the Eastern Carpathians, the BMF composition is dominated by calcite (coccolith debris, cement) and diagenetic silica, with the remainder consisting largely of detrital clays, quartz and minor feldspar. Abundant intervals with soft sediment deformation, likely slump deposits, alternate with thinly layered marls that may locally contain layers and lenses of rippled and cross-laminated sandstone. The latter suggest intermittent action of traction currents. Although the fine grained nature and abundant nanoplankton content of the marls suggest that they originated via pelagic settling through the water column, upon close inspection, they consist of flattened sand-size yet fine-grained aggregates (soft clasts). Experimental studies suggest that these were likely eroded from the seabed and transported in bedload by bottom currents. Inclined fabric elements within marls suggest that soft clasts formed ripples, and that marl layers are the depositional consequence of ripple migration. Whereas typical marl layers probably reflect migration of small ripples of a few cm's height, there are also cross-bedded marly beforms with ca. 20 cm pre-compaction relief that by size are muddy megaripples. Unlike in sand, where bedform hierarchy reflects increasing flow velocity, muddy megaripples more likely are a reflection of bottom current systems of substantial duration. With marl layers as well as interbedded sands recording bottom current activity, the BMF represents a combination of slope processes and bottom current activity. The likely environment of deposition is a lower slope to basin setting with contour currents reworking pelagic sedimentation and intermittent sediment supply by slumping.
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https://authors.elsevier.com/a/1YiM58RVhr791
